Method of coating metal



Dec. 3, 1940. M. scHoN METHOD OF COAIING METAL Filed Aug. 20. 1936 SMQ/YM UHM--,M.-

erated with sheets or stripsof any desired length. This steel has a low carbonyfcontent, e. g., .05 to .10%, and is of a custom aryllthin gauge of about .005 to .015 comparable to the usual tin plate employed for making metalcontainers and container caps. The steely strip is traveled continuously from the coiler Il) under the guide roll I2 into the heating chamber I3 of the annealing furnace, over the roll I4 and through the cooling leg I5.

'I'he lengths of the heating chamber and the cooling leg, the speed of the travel of the strip, and the temperatures maintained within the furnace and the leg are preferably such that the steel is (1) given a bright anneal, and (2) ls cooled to a temperature, preferably in the neighborhood of 1472" F., i. e., the strip leaves the lower end I6 of the leg I5 at a high temperature, preferably above the melting point (about 1250 F.) of aluminum.

The lower end I6 of the leg I5 terminates below the level of a bath o' molten aluminum I1 which as shown is wholly confined and supported between the coating rolls I8 and I9. The coating l rolls also act to propel the stripY through the several instrumentalities of the apparatus.

The annealing operation may be conducted at temperatures above 1500 F. and is preferably conducted in a reducing atmosphere such as hydrogen whereby its surface is cleansed of scale and oxide in accordance with well known practice from which the present invention departs, however, in that I find itvto be an absolute requirement that this cleansing step be carried on at a temperature of at least 1000 F. Ato secure a satisfactory coating and preferably high enough so that the strip will be bright annealed and will have an initial temperature when entering the bath, above that of the bath in accordance with the method hereindescribed. By having the strip enter the bath I1 directly from the leg I5vof the annealing furnace, and below the surfaceof the bath, no opportunity for oxidation of the annealedl strip is presented and, moreover, the hydrogen atmosphere in the leg I5 is available to actv -upon the aluminum in thev bathand prevent anyv formation of objectionable oxide slag about the strip. l

It is anr important feature of the invention as above set forth, that the temperature of the base metal when introduced into the bath is relatively high, namely, around 1500 i. e., higher than that of the temperature of themolten aluminum in the bath I1 which isusually about 1250 to 1325 F. I nd by continuously passing the annealed metal strip'at such a temperature into the bath, for a relatively short distance and at a rapid rate with consequent reduction in the time period of contact betweenthe base and coating metals, and coating the aluminum upon the base lmetal by means of rolls, that a very complete union'between the base metal and the aluminum takes place in which the FezAla is not objectionably present and a ysmooth and uniform coating is produced. v

The coating rolls I8 are operable at various speeds to control the rate of travel oi the strip through the apparatus and are adjustable relative .to each otherl to vary the thickness of the coating. The molten aluminum is fed to the bath from a suitable launder 20. One of the rolls I8 is formed with end flanges ZI cooperating with the nip of therolls to form side Walls for confining the bath. The bath may be provided with means for coating the metal on one side only of the strip. By confining the bath in the nip of the rolls i. e. wholly supported by the rolls, a relatively small volume of molten aluminum is necessary and, consequently, only a short 'time period is required for effecting the coating operation.

Therefore, the initial temperature of the annealed base metal entering the bath, and the speed of travel of the strip is so controlled in cooperation with the relatively short distance required for the strip-to traverse the bath, as to afford a. very brief time period of contact beduces substantially the opportunity for reaction between the iron and aluminum, which is important, since aluminum coated steel heretofore produced has been objectionably characterized by the presence of an alloy or reaction product of the iron and aluminum (Fe2Al3) to the extent that the metal is brittle, and hence not commercially workable for drawing, stamping or pressing of metal products.

'I'he coated product may be drawn,'stamped or pressed to form a variety of shaped articles, for example, containers such as cans or bottles and metal closures such as crown caps without crack: ing of the metal or loosening of the coating, and is generally superior to the usual tin plate ernployed for this purpose. Moreover, the coating is free of spots and is corrosion resistant indicating the absence of an appreciable amount of FezAla in the coated surface. Also since the metal base is introduced at a high temperature, very thin coatings are obtainable, e. g., less than .0012", which are highly desirable.

The strip is ejected by the coating rolls 8 into the atmosphere and the molten coating is hardened by the reduced temperature thereof, the strip being coiled by a coiler 22 into a roll.

If desired, a suitable polishing and smoothing tween the strip and the aluminum. This remeans may be employed to treat the coated strip` after the coating is hardened and before it is coiled, i. e., during its passage from the coating rolls to the coiler.

In some cases, the hardening is produced by a quick cooling through the medium of a conduit having a.. cooling coil and preferably in a nonoxidizing atmosphere. Also, the molten coating strip may be first passed through a non-oxidizing atmosphere at elevated temperature and then into a cooling zone having a non-oxidizing atmosphere. Such treatments in a non-oxidizing atmosphere will avoid the effects of oxidation While the positively applied cooling or chilling will afford a quick hardening, thereby permanently preserving the brilliant mirror-like appearance of the molten coating as it issues from the coating rolls.

While I have described the invention in connection with the coating of steel strip with aluminum, it is equally useful for applying a coating of tin to the base metal. Where tin is used as the coating metal, the bath will have a temperature of about 600 F. and the strip will be heated paratus illustrated and the details of the method` disclosed are merely illustrative and that such variations in the method and apparatus are within the invention as come within the scope of the appended claims.

I claim:

l. The continuous method of annealing and coating steel with one of a group of metals consisting of tin and aluminum comprising annealing the base metal and traveling the same, without opportunity for oxidation, into a molten bath of the coating metal wholly confined and supported between a pair of coating rolls, and rolling the coating metal on the surface of the base metal as it passes between said rolls.

2. The continuous method of annealing and coating steel with aluminum comprising annealing the base metal and traveling the same directly from the annealing treatment and without opportunity for oxidation, into a molten bath of the coating metal wholly confined and supported between a pair of coating rolls, and rolling the coating metal on the surface of the base metal as it passes between said rolls.

3. The method of coating steel with aluminum which comprises introducing steel at a temperature above the melting point of aluminum into a bath of aluminum wholly confined and sup ported between a pair of coating rolls, and coating the steel as it passes between said rolls therewith by rolling the aluminum upon the steel.

4. The method of coating steel with aluminum which comprises introducing steel at a temperature of about 1500 F. into a bath of aluminum wholly confined and supported between a pair of coating rolls, and coating the steel therewith by rolling the aluminum upon the steel as it passes between said rolls.

5. The continuous method of annealing and coating steel with aluminum comprising annealing the base metal and traveling the same, without opportunity for oxidation at an initial temperature above the melting point of aluminum to and through a molten bath of the coating metal Wholly confined and supported betweena pairh'ogf coating rolls, and rolling the coating metal'bn the surface of the base metal as it passes between said rolls.

6. The continuous method of annealing and coating,l steel with aluminum comprising annealing the base `metal and traveling the same, without opportunity for oxidation, at an initial temperature of about 1500 F. to and through a molten bath of the coating metal wholly confined and supported between a pair of coating rolls, and rolling the coating metal on the surface of the base metal as it passes between said rolls.

7. The continuous method of annealing andy coating steel with aluminum comprising bright annealing the base metal and traveling the same, without opportunity for oxidation at an initial temperature of about 1500 F. in and through a molten bath of the coating metal wholly connned and supported between a pair of coating rolls, and rolling the coating metal on the surface of the base member as it passes between said rolls.

8. The method of coating steel with aluminum which comprises annealing the steel and introducing the same at a temperature above the melting point of aluminum into a bath of the coating metal wholly confined and supported between a pair of coating rolls, and coating the steel by rolling the aluminum upon the steel as it passes between said' rolls.

9. The method of coating steel with aluminum which comprises annealing the steel and introducing the same at a temperature of about 1500 F. into a bath of aluminum Wholly confined and supported between a pair of coating rolls and having a temperature of about 1250 F. to 1325 F. and coating the steel by rolling the aluminum upon the steel as it passes between said rolls.

10. The continuous method of annealing and coating steel `with aluminum comprising annealing the steel and controlling the cooling thereof to a temperature above the melting point of aluminum, introducing the annealed steel at such temperature and without opportunity for oxidation into a bath of molten aluminum wholly confined and supported between a pair of coating rolls, and coating the aluminum on the steel by rolling the aluminum upon the steel as it passes between said rolls.

1l. The continuou-s method of annealing and coating steel with aluminum comprising annealing the base metal in a reducing atmosphere at a temperature above 1000 F. and traveling the same, without opportunity of oxidation, into a molten bath of the coating metal Wholly connned and supported between a pair of coating rolls, and rolling the coating metal on the surface of the base metal.

12. The continuou.r method of annealing and coating steel with aluminum comprising annealing the base metal at a temperature above 1500 F. and traveling the same in a non-oxidizing atmosphere into a molten bath of the coating metal wholly confined and supported between a pair of coating rolls, and rolling the coating metal on the surface of the base metal as it passes between said rolls.

13. The continuous method of annealing and coating steel with aluminum comprising annealing the base metal and traveling the same without opportunity for oxidation to a molten bath of the coating metal wholly confined and supported between a pair of coating rolls, introducing the steel at a temperature of substantially 1500 F. below the surface ofv the coating metal in a non-y oxidizing atmosphere, and rolling the coating metal on the surface of the base metal as it passes between said rolls.

MATTHEW SCHON. 

